Automatic value populate on form field, based on selection of another field

I have created table StudentDetails,

In Form,

I have 2 fields on form

Name – it has lookup values to select, it shows all the records(2columsn – name, RegId) in table StudentDetails

RegID  – value to this filed should populate automatically based on “name” selected in above field.

Problem is in my example I have 2 records with same name, If user select second name, then RegID should populate with value “1001”

Any suggestions to handle above scenario.

Thanks